The present invention relates to a device for positioning and joining at an angle the edges of two sheets to be stitched in a sewing machine, particularly for forming a mattress case.
Conventional mattress cases are constituted by an upper sheet and a lower sheet which are rectangular, have rounded corners and are connected one another by a perimetric band.
The band is joined to the sheets by stitching with the aid of a border forming machine which, in practice, is a sewing machine which joins one another the adjacent edges of one sheet and of the perimetric band, with or without interposing a covering tape. Since the sheet is rested horizontally above the mattress body and the band must wrap around the body vertically, in order to achieve a stitched seam that joins one another the contiguous edges of the sheet and of the band the sewing machine is arranged at a 45.degree. angle, so that the needle can pass through both edges and stitch them.
Currently, the edges are positioned manually by operators as sewing progresses. This requires the assigned personnel to be highly skilled and also to perform a significant physical effort, since the sheet and the band must be properly tensioned to avoid forming creases.
Italian Patent No. 1,290,666 by the same Applicant discloses a new device which allows to mutually position the edges of two sheets arranged at 90.degree. to each other, particularly of a sheet and of the perimetric band of a mattress, without requiring any manual intervention. The device is characterized by an angular element comprising a first laminar channel which forms a guide for the edge of the sheet and a second laminar channel which forms a guide for the edge of the band; the channels are arranged at right angles and each channel is comprised between two walls, of which one lies outside the right angle and the other is arranged inside it, and respective through openings are formed in the outer walls; two advancement elements are further provided which comprise rotating heads arranged so as to tangentially engage the sheet and the band through the through openings, in order to arrange the edges of the sheet and of the band, guided in the channels, adjacent to each other.
Problems have occurred with this device when, in order to complete the peripheral stitching of the mattress, it is necessary to remove the abutment of the rotating advancement heads.